[feature request] support older terminals w/ fallbacks for Unicode symbols

[DerekNonGeneric]

After stumbling upon the figures package, I realized that each figure symbol provided by this package should ideally have a fallback for terminals that do not support Unicode. The author of figures has a different idea on what these symbols should be, so we would likely not be able to depend on that package for our uses. It also seems to have more than we would need, but the current lack of fallbacks should probably be addressed by us somehow.